BL-SPL Band Limited-Sound Pressure Level

A full-scale wind tunnel test program was begun to explore the potential of an individual blade control (IBC) system to reduce noise and vibration, and to improve rotor performance of a UH-60 (Black Hawk) helicopter. The first phase of this testing was performed using the U.S. Army/NASA Large Rotor Test Apparatus (LRTA) to operate a full-scale UH-60A rotor in the NASA Ames Research Center 80- by 120-Foot Wind Tunnel. The acquired wind tunnel data set includes measurements of rotor performance, steady and dynamic hub forces and moments, rotor loads, control system loads, and blade vortex interaction (BVI) noise. The LRTA rotor balance was used to assess the level of hub vibration. Both fixed-position and traversing microphones were used to measure the BVI noise. The IBC motions were produced by hydraulic actuators that replaced the normally rigid pitch links of the UH-60 helicopter control system. The actuators were designed by ZF Luftfahrttechnik GmbH to impart up to ±6.0 ° blade pitch input at the 2/rev frequency and up to ±1.6 ° at the 7/rev frequency. In this first phase of the test, the IBC system was not tested to its full authority due to limited test time. Nevertheless, the preliminary wind tunnel data obtained demonstrated overall vibration reductions of 70 % using approximately 1.0 ° of 3/rev IBC, and BVI noise reductions of up to 12 dB (75%